Abstract
Low velocity compressional wave (P-wave), Vp values, have been observed from the lunar geophysical measurements made during the Apollo 14, 16 and 17 missions. These low velocities are attributed to lack of water, low soil compaction as well as the non-consolidated nature of the regolith. The microgravity lunar regolith simulant velocity experiment (µ-SVeLSE) aims to determine if there is any dependence of gravitational force on the seismic longitudinal velocity measurements and thus correlate with data previously determined from in-situ lunar regolith measurements. The experiment is composed of a small cylindrical container and a low power control and data acquisition electronics. No external power source was necessary. The prototype is comprised of a regolith container (22cm x 7cm) with all the data acquisition and control electronics included and working on a low voltage battery power sources. The system, designed by us, produces very minute vibration impulses. The impulses from the source transducer (Tx) are sent during limited temporal windows of emission-reception (10 milliseconds), and recorded as weak sonic-ultrasonic impulses that reach the two receivers (Rx). The system has just a start-stop switch than can be initiated directly by a wireless mechanism. The system records the data on a micro-SD card and weighed, together with the lunar regolith (JSC-1), approximately 1.4 kg. The container is completely closed and designed not to vent any regolith particles. During October 2018 we took the experiment onboard an airborne microgravity campaign, carried out in Ottawa (Canada) by the National Research Council’s Falcon 20 aircraft. We acquired data on three parabolas of between 15 and 30 seconds with low noise microgravity values. Preliminary Vp measurement results, compared with those obtained in Earth’s normal 1g, show variations of signal amplitude that are attributed to lower coupling of the source and receivers to the suspended grains during the micro-g phases of flight. Vp velocity results measured during 1g were around 90 m/s whereas during micro-g phases of flight the velocities apparently decreased.

Abstract

Abstract
The authors wish to make the following erratum to this paper [1]: Equations (1), (7), and (9) are incorrect and must be replaced by the following equations: [Formula presented] The authors apologize for this literal mistake, but emphasize that the content of the article is still correct, since all calculations were performed with the correct equations. The manuscript will be updated and the original will remain online on the article webpage, with a reference to this Erratum.

Abstract
Energy harvesting devices can increase autonomy of submersible marine sensors. However, only the water movements can be used as energy source, since neither solar or temperature gradients are available bellow surface waters. A Linear Electromagnetic Generator (LEG), in a milliwatt energy harvester, is presented. Any moving parts are in contact with water, thus avoiding biofouling problems in the harvester. In this work, a 100mm length, 60mm diameter, cylindrical LEG was designed to maximize output power, and analyzed the effects of magnets size and geometry as well as coils position, at several working conditions. Two coils were used, with an internal resistance of 130 ? in 1500 turns, together with N38-N42 magnets. A mean electrical power of 25 mW (100 mW peak) was experimental measured in the optimized configuration, in realistic conditions, which is enough to power almost any electronic low-power sensor.

Abstract
Salinity measurement in water is typically performed with conductivity sensors. However, for long-term marine deployments, loss of precision is observed, mainly due to electrode drift (oxidation and degradation occurs in the presence of water, salts and bio-fouling), which results in inaccuracy of measurements. A cost-effective, low-power, four-probe salinity sensor is presented, to accurately measure long-term deployments in oceans, rivers and lakes. The four-probe methodology overcomes many of the drift problems, and the use of low-cost stainless-steel electrodes (avoiding platinum or titanium materials) can still achieve good long-term stability, in the practical salinity scale range from 2 to 42 PSU. Low-power electronics (200 µA in sleep-mode and 1 mA in active-mode) based on a ratiometric ADC conversion, and a low-power microcontroller with non-volatile memory, complements the proposed sensor, to achieve an autonomous salinity sensor for long-term marine deployments, with autonomy above 1 year with a 1 min-1 sample rate, using a common 2400 mA x 3.7 V lithium battery.

Abstract
A cost-effective (less than 20€) and low-power device is present for in situ continuous monitoring of suspended sediments (SPM) concentration in estuarine and coastal areas. The sensor uses nephelometric technique for SPM values less than 20g/L and backscatter technique for higher ones. A transmitted infrared (IR) and ultraviolet (UV) channels are used to perform the distinguish of inorganic from organic matter in the suspended particles. It is explained the design and built of the sensor as its calibration and preparation for in field tests. The sensor was deployed for one week in a small dock in the estuarine zone of Cavado river (Esposende, Portugal) where is analyzed the SPM and organic/inorganic matter change with the tidal cycles.